I personally loved the Gingrich trilogy. But then I think alt-history is one of the most interesting genres to explore.
There's also a series entitled "the Lost Regiment" written by his co-writer William R. Forstchen that is also really good. It centers around a regiment of union troops who are transported through a space/time rift to a planet populated by decedents of other people from different periods in time who have also been snatched away. Oh yeah...the planets native population are these giant, warlike, nomadic creatures known collectively as the Horde who have a taste for Humans. 9 books in all tell the story of how this out of place regiment of Yankees help the displaced people of this alien world organize and fight for freedom against the Horde.
I know it sounds pretty far fetched but trust me this series is well written and action packed.

And it is currently being made into a feature film from paramount studios!